In a steam-turbine power station, such water separators have the task of separating in a steam line, in particular before the low-pressure part of the turbine, the water contained in the steam, since when steam is too wet the water drops could cause severe erosion damage to the blading.
Water separators for this purpose are known, for example, from Swiss patent specifications Nos. 440,330 and 621,490. The principle of separation is based on the fact that the steam flow is sharply deflected, usually through 90.degree., in a pipe elbow, in the bend plane of which a row of hollow, curved deflection blades are provided, with the water drops accumulating on the concave blade sides and the water film thus formed being drawn off into the hollow inside of the blade via gaps at the blade outlet edges and/or at the concave blade sides. In these embodiments, if a large amount of water collects locally or if water collects over a considerable time, a portion of the water film can build up at the gap openings and be entrained into the turbine by the steam flow.
A water separator which avoids this disadvantage is described in European patent application No. 0,096, 916. In this water separator, in an otherwise identical arrangement of the row of blades, two rows of bores are provided at the concave blade sides, one in the center and one at the outlet edge of the blades, through which the water film is likewise drawn off into a space of lower pressure. To avoid the entrainment of the water film, cover strips are provided which extend at a distance from the bore rows over their entire length and the rear edge of which, as viewed in the flow direction, is connected in a sealing manner downstream of the bores to the concave side of the respective blade, for example by welding, whereas the front edge, with the concave blade side, forms an inlet gap for the deposited water film, through which the latter is forced into the long, wedge-shaped pocket defined by the cover strip and the concave blade side and is drawn off there via the bore rows. If a large amount of water collects, the water film builds up in the said long pocket without it being possible for a portion of the water to be entrained by the steam.
The suction effect at the bore rows results from the inner space of the deflection blades being connected via their open end faces to an outer housing surrounding the abovementioned pipe elbow, in which outer housing the condensate is separated from the steam, so-called transport steam, which unavoidably passes with the condensate into this outer housing and is fed via an exhaust-steam connecting piece to a point in the steam circuit at which a lower pressure prevails than at the concave side of the deflection blades.
An external pipe is required for discharging the above-mentioned transport steam to the place of application. It has been shown that such a pipe is generally more expensive than the separator itself. This economic aspect has recently been a factor in the reequipping of existing plants, that is replacing obsolete separators, or separators requiring overhaul, by such a newer and more effective type of construction, while power station operators, because of the high costs of the pipe of a separator of the last-mentioned type of construction, decide in favour of a reconstruction of the existing water separator, which reconstruction is slightly cheaper overall, even if less efficient.